High speed electron tunneling devices

ABSTRACT

A detector includes a voltage source for providing a bias voltage and first and second non-insulating layers, which are spaced apart such that the bias voltage can be applied therebetween and form an antenna for receiving electromagnetic radiation and directing it to a specific location within the detector. The detector also includes an arrangement serving as a transport of electrons, including tunneling, between and to the first and second non-insulating layers when electromagnetic radiation is received at the antenna. The arrangement includes a first insulating layer and a second layer configured such that using only the first insulating in the arrangement would result in a given value of nonlinearity in the transport of electrons while the inclusion of the second layer increases the nonlinearity above the given value. A portion of the electromagnetic radiation incident on the antenna is converted to an electrical signal at an output.

RELATED APPLICATION

[0001] The present application is a Continuation of U.S. patentapplication Ser. No. 10/347,534, entitled HIGH SPEED ELECTRON TUNNELINGDEVICES, filed on Jan. 20, 2003, which in turn is a Continuation of U.S.patent application Ser. No. 09/860,972, entitled HIGH SPEED ELECTRONTUNNELING DEVICE AND APPLICATIONS, filed on May 21, 2001, now U.S. Pat.No. 6,563,185, all of which are incorporated herein by reference in itsentirety.

BACKGROUND OF THE INVENTION

[0002] The present invention relates generally to optical devices and,more particularly, to optoelectronic devices based on electrontunneling.

[0003] The increasing speed of optical communications is fueling therace to achieve ever faster optical communications devices fortransmitting, modulating and detecting electromagnetic signals.Terahertz speeds are expected in the near future, and opticalcommunication devices that can operate at such high speeds are in greatdemand.

[0004] A possible approach to achieving high speed optoelectronicdevices for use as optical communication devices is electron tunneling.Electron tunneling-based devices, such as metal-insulator-metal (M-I-M)devices for use as infrared and far-infrared detectors and frequencymixers have been explored in the past (see, for example, S. M. Faris, etal., “Detection of optical and infrared radiation with DC-biasedelectron-tunneling metal-barrier-metal diodes,” IEEE Journal of QuantumElectronics, vol. QE-9, no. 7 (1973); L. O. Hocker, et al., “Frequencymixing in the infrared and far-infrared using a metal-to-metal pointcontact diode,” Applied Physics Letters, vol. 12, no. 12 (1968); and C.Fumeaux, et al., “Nanometer thin-film Ni—NiO—Ni diodes for detection andmixing of 30 THz radiation,” Infrared Physics and Technology, 39(1998)). Such M-I-M devices generally operate on the basis of electronrectification and current production due to incident electromagneticenergy and resulting electron tunneling effects. M-I-M devices cannormally be used to rectify extremely high frequencies, extending intothe optical frequency range.

[0005] In addition to high frequency rectification, it is also desirableto achieve high degrees of asymmetry and nonlinearity in thecurrent-versus-voltage (I-V) curve in electron tunneling devices. Thedifferential resistance of the device, which corresponds to thesensitivity of the device to incoming electromagnetic energy, isdirectly related to the nonlinearity of the I-V curve. However, priorart M-I-M devices generally exhibit low degrees of asymmetry andnonlinearity in the electron transport such that the efficiency of suchdevices is limited. A high degree of nonlinearity improves the quantumefficiency of the electron tunneling device, which is number ofelectrons collected for each photon incident on the M-I-M device. Highquantum efficiency is crucial for efficient operation and highsensitivity of the M-I-M diode in all optoelectronic applications. Forpurposes of this application, a diode is defined as a two-terminaldevice. A high degree of nonlinearity offers specific advantages incertain applications. For example, in optical mixing, second orderderivatives of the current-voltage relationship determine the magnitudeof the signal produced in frequency down-conversion. A higher degree ofasymmetry in the I-V curve between positive values of V (forward biasvoltage) and negative values of V (reverse bias voltage) results inbetter rectification performance of the device. A high degree ofasymmetry is required, for example, to achieve efficient large signalrectification such as in the detection of high intensity incidentfields. In this high intensity field regime, the electron tunnelingdevice functions as a switch, and it is desirable to attain a lowresistance value in one polarity of voltage and a high resistance valuein the opposite polarity of voltage is desired. Alternatively, with lowfield intensities and large photon energies, the incident field sweeps alarger portion of the electron tunneling device dark I-V curve and,consequently, the high asymmetry translates into high responsivity andas well as high quantum efficiency and sensitivity in electromagneticradiation detection.

[0006] The fabrication of the combinations of alternate layers of metalsand insulators in M-I-M-based devices, in comparison to semiconductormaterials, is advantageous due to ease of deposition of materialsrelative to semiconductor fabrication. It has been suggested that therecent trend of decreasing the size of electronic devices to achievehigh speed switching will ultimately make semiconductor-based devicesimpractical due to fluctuation of carrier concentration, which occurswhen semiconductor devices are reduced to mesoscopic regimes (see, forexample, Suemasu, et al., “Metal (CoSi₂)/Insulator(CaF₂) resonanttunneling diode,” Japanese Journal of Applied Physics, vol. 33 (1994),hereafter Suemasu). Moreover, semiconductor devices are generally singlebandgap energy devices. This characteristic of semiconductor devicesmeans that, in detection applications, no current is produced when aphoton having energy less than the bandgap energy is incident on thesemiconductor device. In other words, the response of the semiconductordevice is limited by the bandgap energy. When a semiconductor diode isused to rectify high frequency oscillations, the semiconductor materiallimits the frequency response of the diode because the charge carriersmust be transported through a band, in which concentration are limitedin comparison to a metal.

[0007] Existing electron tunneling devices based on metal-oxidecombinations are generally fabricated by forming a metal layer, exposingthe metal layer for a certain amount of time such that the native oxideof the metal is formed, then repeating the process as desired.Photolithography techniques may also be used to achieve desired shapesand patterns in the metals and insulators. For example, Suemasudescribes a metal (CoSi₂)/insulator(CaF₂) resonant tunneling diode witha configuration M-I-M-I-M-I-M triple-barrier structure for use as longwavelength (far-infrared and milliwave) detectors and emitters. However,the M-I-M-I-M-I-M device of Suemasu is much more complicated than thesimple M-I-M devices, and must be fabricated using a complex epitaxialgrowth procedure using exotic materials. In fact, Suemasu chooses to usethe triple-barrier structure rather than a slightly simplerdouble-barrier structure for apparently better performance results inthe electron tunneling process. Therefore, although the M-I-M-I-M-I-Mdevice of Suemasu achieves much higher degrees of asymmetry andnonlinearity in the I-V curve than the M-I-M devices, the performancegains come at the cost of the simplicity in design and fabrication.

[0008] An alternative approach is the use of a combination of a metaland a semiconductor in a metal-insulator-semiconductor (MIS)configuration (see, for example, T. Yamada, et al., “SemiconductorDevice Using MIS Capacitor,” U.S. Pat. No. 5,018,000, issued 21 May1991). The drawback to currently available MIS devices is also thelimited efficiency due to asymmetry and nonlinearity limitations. MISdevices cannot operate at as high frequencies as M-I-M devices becausethe concentration of electron states in the semiconductor is lower thanthat from a metal.

[0009] At this time, infrared detectors, for example, capable ofreceiving electromagnetic signal at terahertz rates, at roomtemperature, are not readily available, to the Applicants' knowledge.Temperature-controlled alternatives, such as narrow bandgapsemiconductor detectors, and bolometers, exist on the market, but theextra considerations associated with the temperature control mechanismmake such devices expensive and bulky. Prior art M-I-M detectors arecapable of detecting infrared radiation without cooling, but these priorart detectors are not sensitive enough for practical applications.

[0010] As will be seen hereinafter, the present invention provides asignificant improvement over the prior art as discussed above by virtueof its ability to provide the increased performance while, at the sametime, having significant advantages in its manufacturability.

SUMMARY

[0011] As will be described in more detail hereinafter, a number of highspeed electron tunneling devices are disclosed herein. The devices ofthe present invention are especially distinguishable from theaforementioned electron tunneling devices of the prior art by theimplementation of resonant tunneling using at least one layer of anamorphous material in the devices. In a first aspect of the invention, adetector for detecting electromagnetic radiation incident thereon isdisclosed. The detector has an output, exhibits a given responsivity andincludes first and second non-insulating layers spaced apart from oneanother such that a given voltage can be applied across the first andsecond non-insulating layers, the first non-insulating layer beingformed of a metal, and the first and second non-insulating layers beingconfigured to form an antenna structure for receiving electromagneticradiation. The detector further includes an arrangement disposed betweenthe first and second non-insulating layers and configured to serve as atransport of electrons between the first and second non-insulatinglayers as a result of the electromagnetic radiation being received atthe antenna structure. This arrangement includes a first layer of anamorphous material and a second layer of material, configured tocooperate with the first layer of the amorphous material such that thetransport of electrons includes, at least in part, transport bytunneling, and such that at least a portion of the electromagneticradiation incident on the antenna is converted to an electrical signalat the output, the electrical signal having an intensity which dependson the given responsivity. For purposes of this application, anamorphous material is considered to include all materials which are notsingle crystal in structure.

[0012] In a second aspect of the invention, an emitter for providingelectromagnetic radiation of a desired frequency at an output isdescribed. The emitter includes a voltage source, for providing a biasvoltage, and first and second non-insulating layers, whichnon-insulating layers are spaced apart from one another such that thebias voltage can be applied across the first and second non-insulatinglayers. The emitter also includes an arrangement disposed between thefirst and second non-insulating layers and configured to serve as atransport of electrons between the first and second non-insulatinglayers as a result of the bias voltage. This arrangement is configuredto exhibit a negative differential resistance when the bias voltage isapplied across the first and second non-insulating layers. Thearrangement includes a first layer of an amorphous material and a secondlayer of material, which second layer of material is configured tocooperate with the first layer of amorphous material such that thetransport of electrons includes, at least in part, transport by means oftunneling, and such that an oscillation in the transport of electronsresults. This oscillation has an oscillation frequency equal to thedesired frequency, due to the negative differential resistance, andcauses an emission of electromagnetic radiation of the desired frequencyat the output.

[0013] In a third aspect of the invention, a modulator for modulating aninput electromagnetic radiation incident thereon and providing amodulated electromagnetic radiation at an output is described. Themodulator includes a voltage source for providing a modulation voltage,which modulation voltage is switchable between first and second voltagevalues. The modulator also includes first and second non-insulatinglayers spaced apart from one another such that the modulation voltagecan be applied across the first and second non-insulating layers. Thefirst and second non-insulating layers are configured to form an antennastructure for absorbing a given fraction of the input electromagneticradiation with a given value of absorptivity, while a remainder of theinput electromagnetic radiation is reflected by the antenna structure,where absorptivity is defined as a ratio of an intensity of the givenfraction to a total intensity of the input electromagnetic radiation.The modulator further includes an arrangement disposed between the firstand second non-insulating layers and configured to serve as a transportof electrons between the first and second non-insulating layers as aresult of the modulation voltage. This arrangement includes a firstlayer of an amorphous material and a second layer of material, whichsecond layer of material is configured to cooperate with the first layerof the amorphous material such that the transport of electrons includes,at least in part, transport by means of tunneling, with respect to themodulation voltage. The arrangement is configured to cooperate with thefirst and second non-insulating layers such that the antenna exhibits afirst value of absorptivity, when modulation voltage of the firstvoltage value is applied across the first and second non-insulatinglayers, and exhibits a distinct, second value of absorptivity, whenmodulation voltage of the second voltage value is applied across thefirst and second non-insulating layers, causing the antenna structure toreflect a different amount of the input electromagnetic radiation to theoutput as modulated electromagnetic radiation, depending on themodulation voltage. The modulator is configurable to operate as adigital device, in which only discrete, first and second voltage valuesare used, or as an analog device, in which continuous values of voltagebetween the aforedescribed first and second voltage values are used toachieve a continuum of values of absorptivity between the aforementionedfirst and second values of absorptivity.

[0014] In a fourth aspect of the present invention, a modulator assemblyfor receiving a modulation signal, modulating an input electromagneticradiation and providing an output electromagnetic radiation isdescribed. The modulator assembly includes a voltage source forproviding a bias voltage, and first and second non-insulating layers,which non-insulating layers are spaced apart from one another such thatthe bias voltage can be applied across the first and secondnon-insulating layers. The first and second non-insulating layers arealso configured to form a first antenna structure for receiving themodulation signal and converting the modulation signal so received intoa modulation voltage, which modulation voltage is also applied acrossthe first and second non-insulating layers. The modulator assembly alsoincludes an arrangement disposed between the first and secondnon-insulating layers and configured to serve as a transport ofelectrons between the first and second non-insulating layers as a resultof the modulation voltage. The arrangement includes a first layer of anamorphous material and a second layer of material, which second layer ofmaterial is configured to cooperate with the first layer of theamorphous material such that the transport of electrons includes, atleast in part, transport by means of tunneling. The modulator assemblyfurther includes a second antenna structure having an absorptance value,which absorptance value depends on the aforementioned modulationvoltage. The second antenna structure is configured to receive andselectively absorb the input electromagnetic radiation in proportion tothe absorptance value so as to produce the output electromagneticradiation.

[0015] In an fifth aspect of the present invention, a field effecttransistor for receiving an external signal, switching an input signalaccording to the received, external signal and providing an outputsignal is described. The external signal is switchable between a firstvalue and a second value, and the field effect transistor includes adiode structure including a source electrode for receiving the inputsignal and a drain electrode spaced apart from the source electrode suchthat a given voltage can be applied across the source and drainelectrodes. The diode structure further includes an arrangement disposedbetween the source and drain electrodes and configured to serve as atransport of electrons between the source and drain electrodes. Thearrangement includes at least a first layer of an amorphous materialconfigured such that the transport of electrons includes, at least inpart, transport by means of resonant tunneling with a given value of atunneling probability. The field effect transistor also includes ashielding layer at least partially surrounding the diode structure. Thefield effect transistor further includes a gate electrode disposedadjacent to the shielding layer and is configured to receive theexternal signal and to apply the external signal as the given voltageacross the source and drain electrodes such that, when the first valueof external signal is received at the gate electrode, a first signalvalue is provided as the output signal at the drain electrode and, whenthe second value of external signal is received at the gate electrode, asecond signal is provided as the output signal at the drain electrode.

[0016] In a sixth aspect of the present invention, a junction transistoris described. The junction transistor includes an emitter electrode anda base electrode, which is spaced apart from the emitter electrode suchthat a given voltage can be applied across the emitter and baseelectrodes and, consequently, electrons are emitted by the emitterelectrode toward the base electrode. The junction transistor alsoincludes a first tunneling structure disposed between the emitter andbase electrodes. The first tunneling structure is configured to serve asa transport of electrons between the emitter and base electrodes andincludes at least a first layer of an amorphous material configured suchthat the transport of electrons includes, at least in part, transport bymeans of resonant tunneling with a tunneling probability. The tunnelingprobability depends on the given voltage. The junction transistorfurther includes a collector electrode, which is spaced apart from thebase electrode, and a second tunneling structure, which is disposedbetween the base and collector electrodes. The second tunnelingstructure is configured to serve as a transport, between the base andcollector electrodes, of at least a portion of the electrons emitted bythe emitter electrode such that the portion of electrons is collected bythe collector electrode with a collection efficiency and the transportof electrons includes, at least in part, transport by means oftunneling.

[0017] In a seventh aspect of the present invention, an optoelectronicamplification element is described. The optoelectronic amplificationelement is formed by combining the aforementioned field effecttransistor or junction transistor with a detector coupled to the controlelectrode and an emitter coupled to an output. The optoelectronicamplification element is configured such that electromagnetic radiationincident upon the detector generates a voltage across the detector andsubsequently across the control electrodes of the transistor, base andemitter in the case of the junction transistor. The control voltageacross the control electrodes of the transistor in turn controls thebias voltage on the emitting device which may be tuned to emitsubstantially more electromagnetic radiation than the amount initiallyincident upon the device.

[0018] In an eighth aspect of the present invention, an optoelectronicmixer element for simultaneously receiving at least two distinctfrequencies of electromagnetic radiation and producing an output signalhaving a beat frequency, which beat frequency is a combination of saiddistinct frequencies is described. The optoelectronic mixer elementincludes first and second non-insulating layers spaced apart from oneanother such that a given voltage can be applied across the first andsecond non-insulating layers. The first and second non-insulating layersare configured to form an antenna structure for receivingelectromagnetic radiation of the distinct frequencies. Theoptoelectronic mixer element further includes an arrangement disposedbetween the first and second non-insulating layers and configured toserve as a transport of electrons between the first and secondnon-insulating layers as a result of the two distinct frequencies ofelectromagnetic radiation being received at the antenna structure. Thearrangement includes at least a first layer of an amorphous materialsuch that the transport of electrons includes, at least in part,transport by means of resonant tunneling, and such that at least aportion of the electromagnetic radiation incident on the antenna isconverted to the output signal having the beat frequency.

[0019] In a ninth aspect of the resent invention, an electron tunnelingdevice includes first and second non-insulating layers. The first andsecond non-insulating layers are spaced apart from one another such thata given voltage can be applied across the first and secondnon-insulating layers, and the first non-insulating layer is formed of asemiconductor material while the second non-insulating layer is formedof a metal. The electron tunneling device further includes anarrangement disposed between the first and second non-insulating layersand configured to serve as a transport of electrons between the firstand second non-insulating layers. This arrangement includes a firstlayer of an amorphous material such that using only the first layer ofamorphous material in the arrangement would result in a given degree ofnonlinearity in the transport of electrons, with respect to the givenvoltage. However, in accordance with a first aspect of the presentinvention, the arrangement includes a second layer of material, whichsecond layer is configured to cooperate with the first layer ofamorphous material such that the transport of electrons includes, atleast in part, transport by tunneling, and such that the nonlinearity inthe transport of electrons, with respect to the given voltage, isincreased over and above the given degree of nonlinearity.

[0020] In a tenth aspect of the invention, the first non-insulatinglayer in the electron tunneling device is formed of a superconductor.The first non-insulating layer in the electron tunneling device can alsobe formed of a semi-metal or be in a form of a quantum well or asuperlattice.

[0021] In an eleventh aspect of the invention, the arrangement in theelectron tunneling device further includes a third layer of material,which is configured to cooperate with the first layer of the amorphousmaterial and the second layer of material such that the nonlinearity inthe transport of electrons, with respect to the given voltage, isfurther increased over and above the given degree of nonlinearity.

BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The present invention may be understood by reference to thefollowing detailed description taken in conjunction with the drawingsbriefly described below.

[0023]FIGS. 1A-1E are diagrammatic illustrations of high speed,narrowband detectors and a detector array designed in accordance withthe present invention.

[0024]FIGS. 2A-2G are diagrammatic illustrations of high speed emittersand an emitter array designed in accordance with the present invention.

[0025]FIGS. 3A and 3B are diagrammatic illustrations of high speedmodulators designed in accordance with the present invention.

[0026]FIG. 4 is a diagrammatic illustration of a field effect transistordesigned in accordance with the present invention.

[0027]FIG. 5 is a diagrammatic illustration of a junction transistordesigned in accordance with the present invention.

[0028]FIG. 6 is a diagrammatic illustration of an optoelectronicamplification element designed in accordance with the present invention.

[0029]FIG. 7A is a diagrammatic illustration of a high speedoptoelectronic device including one semiconductor layer and one metallayer designed in accordance with the present invention.

[0030]FIGS. 7B-7D are graphs illustrating the schematic conduction bandprofiles of the high speed optoelectronic device of FIG. 7A for variousvoltages applied across the high speed optoelectronic device.

[0031]FIG. 7E is a graph of a typical current-voltage curve for the highspeed optoelectronic device of FIG. 7A.

[0032]FIG. 8 is a diagrammatic illustration of another high speedoptoelectronic device including one superconductor layer and one metallayer designed in accordance with the present invention.

[0033]FIG. 9 is a diagrammatic illustration of still another high speedoptoelectronic device including one quantum well layer and one metallayer designed in accordance with the present invention.

[0034]FIGS. 10A and 10B are diagrammatic illustrations of high speedoptoelectronic devices shown here to illustrate possible positions of athird layer in the arrangement positioned between the non-insulatinglayers.

[0035]FIG. 11 is a diagrammatic illustration of a high speedoptoelectronic device including a fourth layer designed in accordancewith the present invention.

[0036]FIG. 12 is a diagrammatic illustration of a high speedoptoelectronic device including a superlattice structure designed inaccordance with the present invention.

DETAILED DESCRIPTION

[0037] Still another alternative to the M-I-M, M-I-M-I-M-I-M and MISdevices is disclosed in copending U.S. patent application Ser. No.09/860,988 Attorney Docket Number Phiar-P001 of Eliasson and Moddel(Eliasson), which is filed contemporaneously herewith and isincorporated herein by reference. Eliasson discloses an electrontunneling device based on metal-oxide combinations similar to an M-I-Mstructure but including additional layer of an insulator positionedbetween the non-insulating layers. The additional layer of Eliasson isconfigured to increase the nonlinearity, asymmetry and differentialresistance exhibited by the resulting device over and above the valuesof these parameters exhibited by a simple M-I-M device, which does notinclude the additional layer. The concept of tailoring the layering ofthe non-insulating and insulating layers within the electron tunnelingdevice can be extended to achieve heretofore unseen optoelectronicdevices such as narrowband detectors, emitters, modulators andtransistors, including electron tunneling devices. The optoelectronicdevices of the present invention differ from the aforementioned electrontunneling devices of the prior art in that the devices of the presentinvention are characterized by resonance in the tunneling mechanismwhile using at least one layer of an amorphous material. Theoptoelectronic devices of the present invention are illustrated in FIGS.1A-6 and described immediately hereinafter.

[0038] Turning now to the figures, wherein like reference numbers areused to refer to like components, attention is immediately directed toFIGS. 1A-1E, which illustrate schemes for achieving a narrowbanddetector based on the electron tunneling device. FIG. 1A shows adetector 10A, which includes a first non-insulating layer 12 and asecond non-insulating layer 14, in addition to first and secondinsulating layers 16 and 18, respectively. First non-insulating layer12, second non-insulating layer 14, first insulating layer 16 and secondinsulating layer 18 combine to form a diode structure 15. Detector 10Aalso includes antennae 20 and 21. Antennae 20 and 21 can be integrallyformed from first and second non-insulating layers 12 and 14,respectively, or attached separately thereto. Antennae 20 and 21 areconfigured to absorb incident electromagnetic energy (not shown) over aspecific, narrow range of wavelengths. Detector 10A further includes avoltage source 22 for tuning the characteristics of diode structure 15.In this way, detector 10A achieves a narrow reception bandwidth throughthe use of antennae 20 and 21 that absorb energy over a narrow range ofwavelengths.

[0039]FIG. 1B is an edge view of a narrowband detector 10B of thepresent invention, shown here to illustrate an embodiment in which diodestructure 15B is formed of antennae 20B and 21B as first and secondnon-insulating layers with first and second insulating layers 16 and 18disposed therebetween. When electromagnetic radiation 24 is incident onnarrowband detector 10B, electromagnetic radiation 24 is received byantennae 20B and 21B. Antennae 20B and 21B are also configured toreceive input voltage from voltage source 22 such that thecharacteristics of diode structure 15B is tunable.

[0040] Referring now to FIGS. 1C and 1D in conjunction with FIGS. 1A and1B, parallel and series RLC circuits 10C and 10D, respectively,equivalent to the narrowband detector of FIG. 1A or 1B are shown. Inparallel RLC circuit 10C, a box 15C indicates the collection of parallelcomponents equivalent to diode structure 15 or 15B. Inside box 15C, adiode 30, a resistor 32, an inductor 34 and a capacitor 36 are arrangedin parallel as the equivalent circuit representing diode structure 15 or15B. Voltage source 22 is shown parallel to box 15C, to be consistentwith FIGS. 1A and 1B. A box 24C surrounds the components representingthe incident radiation (EM source 40) and the antennae (resistor 42).Similarly, in FIG. 1D, serial RLC circuit 10D includes a box 15Dindicating the collection of series components equivalent to diodestructure 15 or 15B from FIG. 1A or 1B, respectively. A diode 30′, aresistor 32′, an inductor 34′ and a capacitor 36′ are positioned inseries inside box 15D to represent an equivalent circuit for diodestructure 15 or 15B. Again, an EM source 40′ and a resistor 42′ withinbox 24D represent the incident radiation and the antennae, respectively,and a voltage source 22′ is shown to provide a voltage across diode 30′.

[0041] Continuing to refer to FIGS. 1C and 1D, in each case, theequivalent RLC circuit represents components that can be configured intoa resonant circuit which responds optimally only to a limited range offrequencies. The component values can be modified, as known to thoseskilled in the art, to provide response over a desired range offrequencies. For a parallel RLC circuit having a negative differentialresistance ΔR, the oscillation frequency is given by the equation:$\begin{matrix}{\omega = \left\lbrack {\frac{1}{LC} - \frac{1}{\left( {2\left( {\Delta \quad R} \right)C} \right)^{2}}} \right\rbrack^{1/2}} & (1)\end{matrix}$

[0042] For a series RLC circuit having a negative differentialresistance ΔR, the oscillation frequency is given by the equation:$\begin{matrix}{\omega = \left\lbrack {\frac{1}{LC} - \frac{\left( {\Delta \quad R} \right)^{2}}{4L^{2}}} \right\rbrack^{1/2}} & (2)\end{matrix}$

[0043] In other words, the RLC circuit works to limit the receivingbandwidth of the detector. This effect is important in limiting thenoise bandwidth of the detectors of the present invention.

[0044] In particular, for a parallel RLC circuit operating in a regionwhere ΔR is positive, the oscillation frequency ω is as given byEquation 1 above. For positive values of ΔR, the oscillation is dampenedby an exponential factor exp(−1/(ΔR C)), thus yielding a detectionbandwidth of 1/(ΔR C) with quality factor$Q = {\frac{1}{\Delta \quad R}{\left( \frac{L}{C} \right)^{1/2}.}}$

[0045] Similarly, for a series RLC circuit operating in a region whereΔR is positive, the oscillation frequency ω is as given by Equation 2above. For positive values of differential resistance ΔR, theoscillation is dampened by an exponential factor exp(−ΔR/2L), thusyielding a detection bandwidth of ΔR/L with quality factorQ=ΔR(C/L)^(1/2).

[0046] The receiving frequency of the narrowband detector of FIG. 1A or1B is determined by Equation 1 or 2, depending on the physical device.From Equation 1, for small values of L, the 1/LC term again dominates.From Equation 2, for small values of C, the 1/LC term dominates indetermining the allowed oscillation frequencies. Changing the ΔR valueprovides fine adjustments to the allowed oscillation frequency, andhence the sensitivity off the detector. The fine tuning of the actualdetector device of the present invention should take into account boththe series and parallel RLC tuning circuit analyses to determine theactual allowed oscillation frequencies.

[0047] If the detector is not configured as a resonant circuit, alimitation to its frequency response is its ΔRC time constant. Thecapacitance C can be reduced, for example, by modifying the geometry ofthe device. To further decrease the effective ΔRC value, the antenna canbe configured to add an inductive reactance to the diode, compensatingthe capacitive reactance. Alternatively, the inductive component may beadded physically in parallel with the diode.

[0048]FIG. 1E shows a detector array 50 designed in accordance with thepresent invention. Detector array 50 includes a plurality of detectors10E, each of which detectors 10E has a narrowband receptioncharacteristic as described for detector 10A of FIG. 1A (Voltage source22 of each detector 10A is not shown for simplicity). For example, eachdetector 10E can be configured as detector 10B of FIG. 1B, in which theantennae are integrally formed from the first and second non-insulatinglayers forming diode structure 15B. Furthermore, at least some ofdetectors 10E in detector array 50 can be designed to receive differentfrequencies of input radiation such that detector array 50 is capable ofdetecting narrowband radiation over a range of frequencies. Stillfurther, detector array 50 can be configured such that it is capable ofdetecting radiation over an area larger than the area covered byindividual detectors 10E.

[0049] The narrowband detector of FIG. 1A can be modified in a number ofways. For example, the antennae of the narrowband detector can beconfigured to simultaneously receive two or more distinct frequencies ofincident electromagnetic radiation. The diode structure of thenarrowband detector can be further designed to produce an outputelectrical signal having a beat frequency, which is the differencebetween the two incident frequencies. One frequency from a localoscillator may be applied to the antenna, either in the form ofelectromagnetic radiation or in the form of an applied electricalsignal, and a second frequency can be an incident electromagneticradiation. In this way, the narrowband detector can then be used forheterodyne detection capable of detecting high frequency signals thatare faster than the detection capabilities of the electronics throughanalysis of the beat frequency of the output electrical signal.

[0050] Turning now to FIGS. 2A-2G, high speed emitters based on themodified electron tunneling device of the present invention areillustrated. FIG. 2A shows an emitter 10A, which includes a firstnon-insulating layer 112 and a second non-insulating layer 114. Amultilayer tunneling structure 116 is disposed between first and secondnon-insulating layers 112 and 114. First non-insulating layer 112,second non-insulating layer 114, and multilayer tunneling structure 116combine to form a diode structure 115, which directly emitselectromagnetic radiation 126. This emission of electromagneticradiation 126 results from the relaxation of hot electrons (not shown)within diode structure 115 produced directly from an applied voltagefrom voltage source 122, which includes an intrinsic source impedance(not shown).

[0051] Multilayer tunneling structure 116 shown in FIG. 2A can be anysuitable structure which results in diode structure 115 being capable ofproducing electron transport such as, for example, the double insulatorstructure shown in diode structure 15 shown in FIG. 1A. Other multilayertunneling structures can also be incorporated into emitter 100A withoutdeviating from the spirit of the present invention. For example, a thirdinsulator layer can be added to the double insulator structure to forman M-I-I-I-M structure. With the selection of a suitable insulator, aquantum well can formed at both of the insulator-insulator interfaceswith the application of a proper applied voltage. The addition of thisthird insulator layer limits the range of applied voltage values whichyield appreciable current flow, thus resulting in increased nonlinearityin the current-voltage characteristics of the electron tunneling device.As another example, an additional non-insulating layer as well as aninsulator layer such that the device forms the structure M-I-I-M-I-M.The central metal layer can be configured to form a quantum well. Thisquantum well restricts the energy levels at which electrons can traversethe M-I-I-M-I-M structure, thus resulting increased asymmetry at anoptimal value of applied voltage. As still another example, themultilayer structure can be of the form I-M-I-I-M-I-M-M-I-M-I-I suchthat the overall structure takes the form M-I-M-I-I-M-I-M-M-I-M-I-I-M.In this case, the multilayer produces a specific range of allowedenergies for electrons tunneling through the structure which is broaderthan the range of energies allowed by the inclusion of a single isolatedquantum well. In this way, the range of voltages at which resonanttunneling takes place can be tailored for a desired application.

[0052]FIG. 2B illustrates another emitter 100B designed in accordancewith the present invention. Emitter 100B is similar in structure toemitter 100A of FIG. 2A but further includes antennae 120 and 121. Inthe case of emitter 100B, the applied voltage from voltage source 122,or applied current (not shown), biases diode structure 115 in a regionof negative differential resistance, resulting in electronic resonanceeffects. This resonance causes the electron transport between theantennae to oscillate rapidly, thus resulting in the emission ofelectromagnetic radiation from the antennae.

[0053]FIG. 2C is an edge-view of an emitter 100C of the presentinvention, shown here to illustrate an embodiment in which diodestructure 115C is formed of antennae 120C and 121C as first and secondnon-insulating layers with multilayer tunneling structure 116 disposedtherebetween. When a voltage is applied across diode structure 115C byvoltage source 122 such that the diode structure is biased in a regionof negative differential resistance, emitter 100C emits electromagneticradiation from the antennae due to electronic resonance.

[0054] Referring now to FIGS. 2D and 2E in conjunction with FIG. 2B,parallel and series RLC circuits 100D and 100E, respectively, equivalentto the emitter of FIG. 2B are shown. In parallel RLC circuit 100D, a box115D indicates the collection of parallel components equivalent to diodestructure 115. Inside box 115D, a diode 130, a resistor 132, an inductor134 and a capacitor 136 are arranged in parallel as the equivalentcircuit representing diode structure 115 of FIG. 2B. Voltage source 122is positioned parallel to box 15C, to be consistent with FIG. 2B. Aradiating antenna 138 represents antennae 120 and 121. Similarly, inFIG. 2E, serial RLC circuit 100E includes a box 115E indicating thecollection of series components equivalent to diode structure 115 ofFIG. 2B. A diode 130′, a resistor 132′, an inductor 134′ and a capacitor136′ are positioned in series inside box 115E to represent an equivalentcircuit for diode structure 115 with a radiating antenna 138′ and avoltage source 122′ to provide a voltage across diode 130′.

[0055] Continuing to refer to FIGS. 2D and 2E, in each case, theequivalent RLC circuit represents components that can be configured intoa resonant circuit which oscillates optimally only over a limited rangeof frequencies. The component values can be modified, as known to thoseskilled in the art, to provide response over a desired range offrequencies.

[0056] Still referring to FIGS. 2D and 2E, it is noted that theaforedescribed emitters take advantage of the negative differentialresistance exhibited by the electron tunneling device of the presentinvention. By biasing the emitter in the negative differentialresistance region, the voltage across the insulating layers of theemitter oscillates at an oscillation frequency. Subsequently, the outputantenna radiates at the oscillation frequency. By ensuring that theoscillation is uniform, coherent radiation is achieved. Also, bycontrolling the oscillation frequency by controlling the voltage biasand by modifying the device dimensions, the frequency of the radiationcan be controlled. In this way, the emitters of the present inventioncan potentially replace currently available optical sources, such aslasers. The radiation emitted by the emitters of the present inventioncan be readily tailored from the visible frequencies into thefar-infrared by scaling the size of the device. Due to the lowerresistivity of the metal-oxide combination devices in comparison tosemiconductor devices, the emitters of the present invention can be madeto operate at higher frequencies than semiconductor oscillators.

[0057] The emitter oscillation frequency can be controlled, for example,by integrating an RLC circuit into the emitter. The conditions of theoscillation frequency control can be analyzed by considering the emitterin a series RLC circuit or a parallel RLC circuit, as discussed infurther detail immediately hereinafter.

[0058] For a parallel RLC circuit having a negative differentialresistance AR, the oscillation frequency is given by the equation:$\begin{matrix}{\omega = \left\lbrack {\frac{1}{LC} - \frac{1}{\left( {2\left( {\Delta \quad R} \right)C} \right)^{2}}} \right\rbrack^{1/2}} & (3)\end{matrix}$

[0059] Several conclusions can be drawn from Equation 3:

[0060] 1. To achieve high oscillation frequency, the inductance L mustbe small;

[0061] 2. For high oscillation frequency, |ΔR| must be large;

[0062] 3. For high oscillation frequency, given small L and large ΔR,the value of C must be optimized.

[0063] 4. For sufficiently small values of C, the (1/LC) term willdominate, and, within certain limits, the magnitude of |ΔR| will haveonly a small effect on the oscillation frequency ω.

[0064] For a series RLC circuit having a negative differentialresistance ΔR, the oscillation frequency is given by the equation:$\begin{matrix}{\omega = \left\lbrack {\frac{1}{LC} - \frac{\left( {\Delta \quad R} \right)^{2}}{4L^{2}}} \right\rbrack^{1/2}} & (4)\end{matrix}$

[0065] Again, several conclusions can be drawn from Equation 4:

[0066] 1. To achieve high oscillation frequency, the capacitance C mustbe small;

[0067] 2. For high oscillation frequency, |ΔR| must be close to zero—inother words, the negative differential region of the I-V curve should beas nearly vertical as possible;

[0068] 3. For high oscillation frequency, given small C and small ΔR,the value of L must be optimized;

[0069] 4. For sufficiently small values of C, the (1/LC) term willdominate, and, within certain limits, the magnitude of |ΔR| will haveonly a small effect on the oscillation frequency ω.

[0070] The experimental devices so far fabricated in accordance with thepresent may be best modeled either as parallel or as series RLCcircuits. Thus one of the two analyses may be used in optimizing theoscillation frequency of the emitter. In either case, the RLC circuitryacts effectively as integration of a tuning circuit to control theoscillation frequency of the emitter.

[0071] The stability of the oscillation frequency can be achieved, forinstance, by integrating the emitter into a structure havingelectromagnetic feedback, such as a Fabry-Perot cavity, or coupled to adistributed Bragg reflector. The reflected electromagnetic energyprovides a frequency-dependent feedback voltage that stabilizes theoscillation frequency. The mechanism of the oscillation frequencystabilization using this method is similar to stimulated emission from again medium in a laser. Stabilization of the oscillation frequency inthe electron tunneling device of the present invention results from thefact that the electron tunneling device can operate both as an emitterand a receiver. The reflected electromagnetic energy is reabsorbed inthe electron tunneling device to cause a slight shift in the operatingvoltage. The shift in the operating voltage changes the value of thedifferential resistance exhibited by the device, thus causing a shift inthe oscillation frequency. In this way, the feedback mechanism works tostabilize the oscillation frequency of the device.

[0072] A possible implementation of the aforedescribed feedbackmechanism is illustrated in FIG. 2F. FIG. 2F shows an emitter 100Ecoupled to an optical fiber 140 having an integrated distributed Braggreflector (DBR), indicated by box 142. DBR 142 is configured to reflectelectromagnetic radiation of a particular wavelength, which is partiallyreabsorbed by the emitter and stabilizes the emission wavelength (i.e.,frequency) to a desired value. Thus, the oscillation frequency ofemitter 100E is stabilized.

[0073]FIG. 2G shows an emitter array 150 designed in accordance with thepresent invention. Emitter array 150 includes a plurality of emitters100G, each of which emitters 100G having a narrowband emissioncharacteristic as described for emitter 100B of FIG. 2B (Voltage source122 of each emitter 100B is not shown for simplicity). For example, eachemitter 100G can be configured as detector 100C of FIG. 2C, in which theantennae are integrally formed from the first and second non-insulatinglayers forming diode structure 115C. Furthermore, at least some ofemitters 100G in emitter array 150 can be designed to emit differentfrequencies of radiation such that emitter array 150 is capable ofproducing narrowband radiation over a range of frequencies. Stillfurther, emitter array 150 can be configured such that it is capable ofemitting radiation over an area larger than the area covered byindividual emitters 100G. Moreover, emitter array 150 can be configuredwith feedback between elements to provide coherent emission across thearray.

[0074] Returning briefly to FIG. 1A, a possible modification ofnarrowband detector 10A is to configure antennae 20 and 21 to reflect orabsorb the incident electromagnetic energy according to the value ofdynamic resistance exhibited by the detector, where the dynamicresistance is inversely proportional to the slope of the I-V curve ofthe device. Noting that the dynamic resistance exhibited by narrowbanddetector 10A is a strong function of bias voltage (as shown in FIG. 7E)applied to the device by voltage source 22, it is readily apparent thatthe incident electromagnetic energy is reflected when the dynamicresistance is very low or very high, and, at immediate values of dynamicresistance, when the dynamic resistance is matched to the antennaimpedance, the electromagnetic energy is absorbed. The absorbedelectromagnetic energy is converted to DC electrical power due to theelectrical rectification effect of the narrowband detector. Since theelectromagnetic energy absorption/reflection can be modulated bychanging the applied bias voltage, the narrowband detector of thepresent invention can function as a modulator by monitoring theelectromagnetic energy reflected by the device. Since the narrowbanddetector of the present invention operates at the frequency of theincident electromagnetic energy, the modulation rate is limited only bythe rate at which the bias voltage can be applied to the device. Therate of applied bias voltage is a function of the RC time constant ofthe device and the signal transmission time, and the RC time constant inthe devices of the present invention can be made very small since thecapacitance of each of the devices can be made very small by virtue ofits dimensions. To further decrease the effective RC value, the antennacan be configured to add an inductive reactance to the diode,compensating the capacitive reactance. Alternatively, the inductivecomponent may be added physically in parallel with the diode.

[0075] The antenna structure can also be tailored to absorb 70% or moreof the incident electromagnetic energy (see, for example, Z. B. Popovic,et al., “A low-profile broadband antenna for wireless communications,”Sixth IEEE International Symposium on Personal, Indoor and Mobile RadioCommunications (PIMRC'95) Wireless: Merging onto the InformationSuperhighway (Cat. No. 95TH8135), vol. (xxvii+xxiii+1389), 135-9,vol. 1. Using such an antenna structure, the modulator of the presentinvention can be made to switch between up to 70% and 0% absorption toachieve a contrast ratio of 2.3 or better. Such a contrast ratio valueis acceptable for various applications such as electromagnetic signalmodulation. Such modulators may be combined in series to provide greaterdepth of modulation.

[0076] Furthermore, the dimensions of the antenna structure and theelectron tunneling device area can be made to range from sub-microns upto hundreds of microns and more, with the result that the wavelength atwhich the modulation occurs can be selected over a large range.Therefore, by modifying the antenna design and scaling the antennadimensions, the modulator of the present invention can be made tofunction over a wide range of wavelengths. In addition, the array ofdetectors shown in FIG. 1E can be made to function as an array ofmodulators by proper antenna design. Since the amount of voltagerequired to bias each modulator in a region of high absorption rangesfrom a fraction of a volt up to just a few volts, arrays of modulatorscan be coupled, for example, to a charge-coupled device. In this way,the modulator array can function as a spatial light modulator.

[0077] Additional modifications to the modulator can be made. Forexample, a second antenna can be added to each modulator such that thesecond antenna, perhaps tuned to a different polarization or wavelength,can be optically addressed to be set to reflect or absorb incidentelectromagnetic energy. Also, by operating the device in the region ofnegative differential resistance (i.e., the negative slope region of theresonance peak), a substantial gain can be added to the dc voltagegenerated in the electronic rectification process. Thus, the modulatorsof the present invention exhibit extremely fast response, broad regionof operation extending from the visible to the far-infrared, lowoperating voltage and an adequate modulation ratio.

[0078]FIGS. 3A and 3B are illustrations of the aforedescribed modulatorsof the present invention. FIG. 3A illustrates a broadband modulator 200Aincluding broadband, receiving antennae 220A and 221A as well asbroadband, modulating antennae 222A and 223A. Receiving antennae 220Aand 221A detect a first electromagnetic radiation 201A incident thereonand produces a voltage across a diode structure 210A. Diode structure210A can be, for example, diode structure 15 shown in FIG. 1A or diodestructure 115 as shown in FIG. 2A or 2B. The induced voltage acrossdiode structure 210A subsequently alters the resistance, capacitance, orresponsivity of the diode structure, which in turn modifies theabsorption characteristics of modulating antennae 222A and 223A. As aresult, modulation antennae 222A and 223A act to modulate a secondelectromagnetic radiation 202A, thus re-emitting second electromagneticradiation 202A toward an output (not shown) as an output electromagneticradiation 203A. Consequently, first electromagnetic radiation 201Areceived at the receiving antenna acts to modulate secondelectromagnetic radiation 202A which interacts with the modulatingantenna to r re-emit output electromagnetic radiation 203A.

[0079] The detecting and modulating antennas of a modulator of thepresent invention can be broadband, as shown in FIG. 3A, narrowband, ora combination thereof FIG. 3B illustrates the use of narrowband antennaefor both emitting and receiving antennae. A narrowband modulator 200Bincludes a diode structure 210B, narrowband, receiving antennae 220B and221B as well as narrowband, modulating antennae 222B and 223B. Diodestructure 210B can again be in the form, for example, of diode structure15 shown in FIG. 1A or diode structure 115 of FIG. 2A or 2B. Narrowbandmodulator 200B operates in essentially the same way as broadbandmodulator 200A of FIG. 3A with a difference in that, since the receivingand modulating antennae are configured to function over a narrow rangeof frequencies, narrowband modulator 200B works as a modulator only inthe narrow range of frequencies. Such a narrowband modulator is usefulin certain applications such as optical communications. The modulator ofthe present invention is configurable to operate as a digital device, inwhich the receiving antennae produces only discrete, voltage valuesacross the diode structure. Alternatively, the modulator is alsoconfigurable as an analog device, in which the receiving antennae isconfigured to cooperate with the diode structure to produce continuousvalues of voltages such that the absorption characteristics of themodulating antennae can be modulated over a continuum of absorptivityvalues.

[0080] Referring now to FIG. 4, a field effect transistor 300 designedin accordance with the present invention is illustrated. Field effecttransistor 300 includes a substrate, on which other components aredeposited. Field effect transistor 300 further includes a sourceelectrode 312 and a drain electrode 314 with first and second insulatinglayers 316 and 318, respectively, disposed therebetween. First andsecond insulating layers 316 and 318 can be replaced, for example, by amultilayer tunneling structure, such as multilayer tunneling structure116 as described in the context of FIG. 2A. A passivation layer 320separates the source and drain electrodes and the first and secondinsulating layers from a gate electrode 322, which is configured toallow the application of a voltage to modulate the potential (not shown)in first and second insulating layers 316 and 318. The modulation of theelectric field within the first and second insulating layers is a resultof the change in the tunneling probability of electrons flowing throughthe multilayer oxide between the source and drain electrodes due to theapplication of the voltage to the gate electrode. Unlike semiconductortransistors, field effect transistor 300 is based on the mechanism ofelectron tunneling, rather than electron and hole transport in asemiconductor band. Therefore, field effect transistor 300 can operateat much higher frequencies than the presently available semiconductortransistors.

[0081] Turning to FIG. 5, a junction transistor 400 designed inaccordance with the present invention is illustrated. Junctiontransistor 400 includes an emitter electrode 412, a base electrode 414and a collector electrode 416. A first multilayer tunneling structure418 is disposed between the emitter and base electrodes. A secondmultilayer tunneling structure 420 is disposed between the base andcollector electrodes. As known to one skilled in the art, junctiontransistors use bias voltages or currents from an external bias source(not shown) to set the operating point of the transistor, and power todrive the output. These external bias sources are configured to applyvoltage, for example, in a common emitter configuration, as a potentialat the base-emitter junction and/or as a potential at thecollector-emitter junction. For instance, a bias source can be used toapply a voltage across the emitter and base electrodes to control thepotential in first multilayer tunneling structure 418 and, consequently,the tunneling probability of electrons from emitter electrode 412 tobase electrode 414. Once emitted, electrons tunnel through firstmultilayer tunneling structure 418, base electrode 414, secondmultilayer tunneling structure 420 and finally into collector electrode416 with a given value of collection efficiency. The collectionefficiency is a function of the fraction of electrons that tunnelunimpeded through the base. The tunneling probability is determined bythe applied voltage to the base, along with other material properties.Again, unlike semiconductor transistors, junction transistor 400 isbased on the mechanism of electron tunneling, rather than electron andhole transport in a semiconductor band. Therefore, junction transistor400 can operate at much higher frequencies than the presently availablesemiconductor transistors.

[0082] A number of the optoelectronic devices described above can becombined to form other optoelectronic components. For example, in FIG.6, an optoelectronic amplification element 500 is described.Optoelectronic amplification element 500 includes a transistor element,represented by a box 510. Suitable transistor element for use inoptoelectronic amplification element 500 are, for example, theaforementioned field effect transistor of FIG. 4 and the junctiontransistor of FIG. 5. Optoelectronic amplification element furtherincludes a detector 512, which is coupled to a control electrode (thegate or base electrode, depending on the transistor type) of thetransistor, and an emitter 514 for generating electromagnetic radiation518. In optoelectronic amplification element 500 shown in FIG. 6,electromagnetic radiation 516 incident upon the detector generates avoltage at the detector and, subsequently, across the control electrodesof the transistor (for example, across the base and emitter electrodesfor a junction transistor). As known to one skilled in the art,transistors use power from an external bias source (not shown) to drivean output, here shown as emitter 514. In this way, the generated voltageacross the control electrodes of the transistor in turn alters the biasvoltage on emitter 514, which can be tuned to emit substantially moreelectromagnetic radiation than the amount initially incident upon thedevice.

[0083] Turning now to FIGS. 7A-7E, possible modifications to the highspeed optoelectronic devices of the present invention are described. Theco-pending application of Eliasson discloses the possibility of using adifferent metal to form each of the non-insulating layers as well asdifferent amorphous insulators as the first insulating layer and thesecond layer of material. However, although the electron tunnelingdevice disclosed in Eliasson is suitable for solar energy conversionapplications, it is possible to further enhance the flexibility of theEliasson device by incorporating materials other than metals into theelectron tunneling device of Eliasson. Furthermore, the devices of thepresent invention are especially distinguishable from the electrontunneling devices of the prior art, such as the M-I-M, M-I-M-I-M-I-M andM-I-I-S devices, by the use of resonant tunneling using at least onelayer of an amorphous material in the devices. Several suchmodifications are discussed immediately hereinafter.

[0084]FIG. 7A illustrates a high speed, optoelectronic device 600. LikeEliasson, optoelectronic device 600 includes first and secondnon-insulating layers 612 and 14, respectively, with a first insulatinglayer 16 of an amorphous material and a second layer 18 of a materialpositioned therebetween. First non-insulating layer 612 and secondnon-insulating layer 14 are spaced apart such that a given voltage canbe provided therebetween. The given voltage can be, for instance, a biasvoltage from an external voltage source (not shown) that is directlyapplied to the first and second non-insulating layers. First insulatinglayer 16 can be, for example, a native oxide of first non-insulatinglayer 612. For instance, if a layer of chromium is used as firstnon-insulating layer 612, the layer of chromium can be oxidized to forma layer of chromium oxide to serve as first insulating layer 16. Othersuitable materials include, but are not limited to, silicon dioxide,niobium oxide, titanium oxide, aluminum oxide, zirconium oxide, tantalumoxide, hafnium oxide, yttrium oxide, magnesium oxide, silicon nitrideand aluminum nitride. In contrast to Eliasson, first non-insulatinglayer 612 of optoelectronic device 600 is formed of a semiconductorwhile second non-insulating layer 14 is formed of a metal.Optoelectronic device 600 is useful in applications such as detectors,in which specific characteristics of the semiconductor positivelycontribute to the detector efficiency. In addition, optoelectronicdevice 600 generally exhibits the high nonlinearity and asymmetry in theelectron conduction, including resonant tunneling, as demonstrated inthe Eliasson device, without the complicated structure of theM-I-M-I-M-I-M device of Suemasu. As an alternative, a semi-metal can beused as first non-insulating layer 612 rather than a semiconductor. Asemiconductor in place of one of the metal electrodes allows furthertailoring of the diode performance by introducing a band gap in thedensity of states in one electrode. The density of states, for example,permits enhanced negative differential resistance, resulting from theprovided voltage shifting the source of tunneling of electrons throughresonant energy levels from regions of high electron concentration(conduction band) to regions of no electron concentration (bandgap). Asemiconductor provides electrons that are more confined in energy thandoes a metal, and therefore the negative differential resistance isenhanced. Furthermore, a semimetal, in place of one of the metalelectrodes, provides yet another source of electrons within a confinedenergy range for the emitting electrode.

[0085] Continuing to refer to FIG. 7A, second layer 18 is formed of apredetermined material, which is different from first insulating layer16 and is configured to cooperate with first insulating layer 16 suchthat first insulating layer and second layer 18 serve as a transport ofelectrons between the first and second non-insulating layers. Thepredetermined material, which forms second layer 18, can be, forexample, an amorphous insulator such as, but not limited to, chromiumoxide, silicon dioxide, niobium oxide, titanium oxide, aluminum oxide,zirconium oxide, tantalum oxide, hafnium oxide, yttrium oxide, magnesiumoxide, silicon nitride, aluminum nitride and a simple air or vacuum gap.Preferably, second layer 18 is formed of a material having asignificantly lower or higher work function than that of first amorphouslayer such that the device exhibits an asymmetry in the energy banddiagram.

[0086] Had the optoelectronic device consisted of only the first andsecond non-insulating layers and the first insulating layer, the devicewould be essentially equivalent to a prior art M-I-M-based device andwould exhibit a given degree of nonlinearity, asymmetry and differentialresistance in the transport of electrons. However, the inclusion ofsecond layer 18, surprising and unexpectedly, results in increaseddegrees of nonlinearity and asymmetry over and above the given degree ofnonlinearity and asymmetry while the differential resistance is reduced,with respect to the given voltage. In addition, the use of thesemiconductor or semimetal as the first non-insulating layer 612 furtherenhances the device efficiency. The increase in the nonlinearity andasymmetry and reduction in differential resistance is achieved withoutresorting to the use of epitaxial growth techniques or crystallinelayers of the aforedescribed prior art. The mechanism of this increaseis described immediately hereinafter in reference to FIGS. 7B-7E.

[0087] Referring to FIGS. 7B-7D in conjunction with FIG. 7A, a schematicof a energy band profile 620 corresponding to electron tunneling device600 and the changes in the energy band profile due to voltageapplication are illustrated. Energy band profile 620 includes fourregions corresponding to the four layers of electron tunneling device600. Energy band profile 620 represents the height of the Fermi level inthe non-insulating layers and the height of the conduction band edge infirst insulating layer 16 and second layer 18 (y-axis 622) as a functionof distance (x-axis 624) through optoelectronic device 600 in theabsence of provided voltage across the device. FIG. 7C illustrates afirst modified energy band profile 630 when a voltage is provided in areverse direction to M-I-M device 600. The voltage may be provided by,for example, an applied external voltage or an induced voltage due tothe incidence of electromagnetic energy. In the case shown in FIG. 7C,the primary mechanism by which electrons travel between the first andsecond non-insulating layers is tunneling in a reverse direction,represented by an arrow 636. In contrast, when a forward bias voltage isprovided, a second modified energy band profile 640 results, as shown inFIG. 7D. In the case of the situation shown in FIG. 7D, tunneling of theelectrons occurs along paths 646 and 646′, but there now exists aquantum well region through which resonant tunneling occurs, as shown byarrow 648. In the region of resonant tunneling, the ease of transport ofelectrons suddenly increase, therefore resulting in increased currentbetween the non-insulating layers of electron tunneling device 600.

[0088] Continuing to refer to FIG. 7D, the addition of second layer 18provides a path for electrons to travel through the device by a resonanttunneling rather than the ordinary tunneling process of the prior artM-I-M device. As a result, more current flows between the non-insulatinglayers of electron tunneling device 600, as compared to the M-I-Mdevice, when a positive voltage is provided while the current flow witha negative voltage provided to the electron tunneling device of thepresent invention. The presence of resonant tunneling in electrontunneling device 600 therefore results in increased nonlinearity andasymmetry with decreased differential resistance in comparison to theprior art M-I-M device.

[0089] A typical I-V curve 650 corresponding to electron tunnelingdevice 600 is shown in FIG. 7E. I-V curve 650 demonstrates that electrontunneling device 600 functions as a diode, where the diode is defined asa two-terminal electronic element. Furthermore, I-V curve 650 is shownto include a resonance peak 656 corresponding to the provided voltageregion in which resonant tunneling occurs. The appearance of resonanttunneling in actually fabricated devices of the present inventiondepends on the precision of the fabrication process. Even when resonancepeak 656 is not present, I-V curve 650 exhibits a higher degree ofasymmetry and nonlinearity in comparison to the I-V curve of a prior artM-I-M device (for example, as shown in FIG. 1E of Eliasson). In otherwords, while the presence of a resonance peak in the I-V curve of anelectron tunneling device of the present invention may lead toadditional advantages in certain applications, such as greatly increasednonlinearity around the resonance peak, the electron tunneling device ofthe present invention achieves the goal of increased asymmetry andnonlinearity with reduced differential resistance in thecurrent-to-voltage performance even when the averaging effect of theamorphous layer “washes out” the resonance peak. Therefore, electrontunneling device 600 essentially includes all of the advantages of theprior art M-I-M-I-M-I-M device, without the complicated fabricationprocedure and the use of exotic materials, and all of the advantages ofthe prior art SIIS device, without the drawbacks of the use ofsemiconductor materials as described above. Despite and contrary to theteachings of Suemasu, the electron tunneling device of the presentinvention is able to achieve increased nonlinearity and asymmetry anddecreased differential resistance in the transport of electrons throughthe device, using readily available metals and insulators in a simplestructure that is simply manufactured compared to the more complexmanufacturing processes of the prior art.

[0090] Referring now to FIGS. 8 and 9 in conjunction with FIG. 7A, morepossibilities for materials are described. An optoelectronic device 700of FIG. 8 includes a modification from the optoelectronic device of FIG.7A in that first non-insulating layer 712 is now formed of asuperconductor. In contrast, an optoelectronic device 800 of FIG. 9includes a first non-insulating layer 812 in a form of a quantum well.The quantum well is contacted appropriately on its edge or through abarrier layer (not shown), as known to those skilled in the art. Theinclusion of the different materials in optoelectronic devices 700 and800 leads to different conduction band diagrams and, hence, differentelectron tunneling properties. Optoelectronic devices 700 and 800 dostill exhibit resonant tunneling with the appropriate applied voltage,but the exact shape of the I-V curve can be tailored according to theapplication by adjusting the material properties of the superconductorand the quantum well, respectively. Superconductor layers enhanceM-I-I-M device by providing non-linearity at extremely low providedvoltages. This is made possible by the relatively small provided voltagerequired to induce the tunneling of quasi-particles. Furthermore,superconductors can provide lower resistance to the device, which canreduce resistance losses.

[0091] In the optoelectronic devices shown in FIGS. 7A-9, it is alsopossible to have a current flow by the mechanism of hot electrontunneling, in which no external voltage is needed. In hot electrontunneling, electrons tunnel from the first non-insulating layer to thesecond non-insulating layer, and vice versa, without the application ofa voltage across the non-insulating layers. This process is useful inapplications where antennas are not used to couple the electric fieldacross the oxide of the diode and the electromagnetic radiation exciteselectrons directly within the electrodes, and also when the energies ofthe incident photons are substantially larger than the barrier providedby the insulating multilayer tunneling barrier.

[0092] Turning now to FIGS. 10A and 10B, optoelectronic devicesincluding a third layer are illustrated. Optoelectronic devices 900A and900B each includes a first and second non-insulating layers 912 and 14,respectively, with first and second insulating layers 16 and 18,respectively, positioned therebetween. First and second non-insulatinglayers can be a metal, semiconductor, semi-metal, superconductor,quantum well, superlattice or a combination thereof. Furthermore,optoelectronic devices 900A and 900B include third layers 920A and 920B,respectively. Third layer 920A is shown to be located between secondinsulating layer 18 and second non-insulating layer 14 in FIG. 10A,while third layer 920B is shown between first and second insulatinglayers 16 and 18, respectively. In either case, the third layer isconfigured such that the nonlinearity and asymmetry in the I-V curve ofthe respective optoelectronic device are further increased over a devicewith just the first two insulating layers. The presence of the thirdlayer functions to enhance the electron tunneling between the first andsecond non-insulating layers by providing an additional path throughwhich the electrons are transported by resonant tunneling. With theapplication of an appropriate voltage across the first and secondnon-insulating layers of the device including the third layer, two pathsexist through which the electrons can potentially travel by resonanttunneling. By matching the two paths, the electron transport is enhancedin comparison to the optoelectronic device with only one or no resonanttunneling paths, thus increasing the degree of nonlinearity andasymmetry in the I-V curve. In other words, the addition of this thirdlayer further limits the range of applied voltage where appreciablecurrent flows, resulting in increased nonlinearity. The third layer canbe, for example, a third insulator, a third non-insulating layer (suchas a metal, semiconductor, semi-metal, superconductor, superlattice or aquantum well) formed by known techniques such as sputtering or atomiclayer deposition. If the third layer, for example, is a quantum well,the result is discrete allowed energy levels. By matching up the allowedenergy level within the quantum well, by a provided voltage, to thoseproduced within the first and second insulating layers, an increasedtunneling current between the two non-insulating layers is produced. Aswith a semiconductor, a superlattice provides electrons that are highlyconfined in energy, and therefore the negative differential resistanceis enhanced.

[0093] Further extending the idea of additional layers between thenon-insulating layers, FIGS. 11 and 12 illustrate optoelectronic devices1000 and 1100, respectively, with further enhanced resonant tunneling bythe addition of a plurality of layers between first and secondnon-insulating layers. Optoelectronic device 1000 of FIG. 11 includes athird non-insulating layer 1020 and a third insulating layer 1022between a first non-insulating layer 1012 and second non-insulatinglayer 14, in addition to first and second insulating layers 16 and 18,respectively. The addition of third non-insulating layer 1020 and thirdinsulating layer 1022 serves to create additional resonance peaks in theI-V curve or to fine tune the location of the original resonance peak inthe I-V curve of optoelectronic device 1000. Taking this idea a stepfurther, optoelectronic device 1100 of FIG. 12 includes a plurality ofadditional, alternating non-insulating layers 1112 and barrier layers1116 cooperating to form a superlattice structure. The superlatticeallows one to perform bandgap engineering and define the energy regionsof highly confined electrons. For example, it is possible to develop aregion with designed bands of electrons and holes and band gaps.Thereby, we are not limited to the material properties of readilyavailable materials.

[0094] Although each of the aforedescribed embodiments have beenillustrated with various components having particular respectiveorientations, it should be understood that the present invention maytake on a variety of specific configurations with the various componentsbeing located in a wide variety of positions and mutual orientations andstill remain within the spirit and scope of the present invention.Furthermore, suitable equivalents may be used in place of or in additionto the various components, the function and use of such substitute oradditional components being held to be familiar to those skilled in theart and are therefore regarded as falling within the scope of thepresent invention. For example, the exact materials used in theaforedescribed devices may be modified while achieving the same resultof high speed optoelectronic devices. Also, the various optoelectronicdevices described above can be combined to form a high speedoptoelectronic integrated circuit, which would have advantages of speed,purely optoelectronic input/output, response from the visible throughthe far-infrared range, scalability and greater ease of fabrication withless toxic materials in comparison to semiconductor integrated circuits.Furthermore, the present invention can also be used as a basis for otherapplications such as, but not limited to, memory, charge-coupled device(CCD), electronically-addressed spatial light modulator (EASLM),optically-addressed spatial light modulator (OASLM), high speedelectronic components, integrated circuits, millimeter wave detector,heat sensor (long wave infrared detectors), frequency converter,multiplexer, demultiplexer and combinations thereof. For example, anoptoelectronic mixer element for simultaneously receiving at least twodistinct frequencies of electromagnetic radiation and producing anoutput signal having a beat frequency, which beat frequency is acombination of said distinct frequencies can be formed. Theoptoelectronic mixer element includes a multilayer structure (such asthe aforedescribed double insulator structure) positioned between a pairof non-insulating layers, which are configured to form an antennastructure for receiving electromagnetic radiation of the two distinctfrequencies. The multilayer structure is configured to serve as atransport of electrons between the pair of non-insulating layers as aresult of the two distinct frequencies of electromagnetic radiationbeing received at the antenna structure. The electron transport occursat least in part by resonant tunneling such that at least a portion ofthe electromagnetic radiation incident on the antenna is converted to anoutput signal having the beat frequency. Such an optoelectronic mixercan be used simply to produce an output beat signal having a beatfrequency such that the output beat signal is a “mix” of the two inputsignals. Mixing allows the detection of the lower beat frequencies ofhigh frequency signals that are faster than the detection capabilitiesof conventional electronic detectors. The element can also be used forheterodyne detection of information encoded on a high frequency carriersignal. The information may be extracted by mixing the high frequencysignal with the output from a local oscillator of the same carrierfrequency. Therefore, the present examples are to be considered asillustrative and not restrictive, and the invention is not to be limitedto the details given herein but may be modified within the scope of theappended claims.

What is claimed is:
 1. A detector for detecting electromagneticradiation incident thereon over a desired range of frequencies, saiddetector having an output and exhibiting a given responsivity, saiddetector comprising: a voltage source for providing a bias voltage;first and second non-insulating layers spaced apart from one anothersuch that the bias voltage can be applied across the first and secondnon-insulating layers, wherein the first non-insulating layer is formedof a metal, and wherein said first and second non-insulating layers areconfigured to form an antenna structure for receiving saidelectromagnetic radiation over the desired range of frequencies anddirecting said electromagnetic radiation to a specific location withinthe detector; and an arrangement disposed between the first and secondnon-insulating layers at said specific location and configured to serveas a transport of electrons between and to said first and secondnon-insulating layers as a result of the electromagnetic radiation beingreceived at the antenna structure, said arrangement including at least afirst insulating layer configured such that using only said firstinsulating layer in the arrangement would result in a given value ofnonlinearity in said transport of electrons, with respect to said biasvoltage, and said arrangement further including a different, secondinsulating layer disposed directly adjacent to and configured tocooperate with said first insulating layer that said nonlinearity, withrespect to said bias voltage, is increased over and above said givenvalue of nonlinearity by the inclusion of said second insulating layerwithout the necessity for any additional layers, and said arrangementbeing further configured such that the transport of electrons includes,at least in part, transport by means of tunneling, and such that atleast a portion of the electromagnetic radiation incident on the antennastructure is converted to an electrical signal at the output, saidelectrical signal having an intensity which depends on the givenresponsivity.
 2. The detector of claim 1 wherein the given responsivityis a function of the bias voltage, and wherein the bias voltage isadjustable such that the given responsivity is consequently adjustable.3. The detector of claim 1 wherein the antenna structure is furtherconfigured to simultaneously receive two distinct frequencies ofelectromagnetic radiation such that the electrical signal has afrequency equal to a difference between the two distinct frequencies. 4.An emitter for providing electromagnetic radiation of a desiredfrequency at an output, said emitter comprising: a voltage source forproviding a bias voltage; first and second non-insulating layers spacedapart from one another such that the bias voltage can be applied acrossthe first and second non-insulating layers; and an arrangement disposedbetween the first and second non-insulating layers and configured toserve as a transport of electrons between and to said first and secondnon-insulating layers as a result of the bias voltage, said arrangementincluding at least a first insulating layer configured such that usingonly said first insulating layer in the arrangement would result in agiven value of negative differential resistance when the bias voltage isapplied across the first and second non-insulating layers, with respectto said bias voltage, and a different, second insulating layer disposeddirectly adjacent to and configured to cooperate with said firstamorphous insulating layer such that said negative differentialresistance, with respect to said bias voltage, is decreased below saidgiven value of negative differential resistance by the inclusion of saidsecond insulating layer without the necessity for any additional layers,and said arrangement being further configured such that the transport ofelectrons includes, at least in part, transport by means of tunnelingsuch that an oscillation in the transport of electrons results, saidoscillation having an oscillation frequency equal to the desiredfrequency due to the negative differential resistance and causing anemission of electromagnetic radiation of the desired frequency at theoutput.
 5. The emitter of claim 4 wherein said first and secondnon-insulating layers are configured to form an antenna structure foraiding in the emission of said electromagnetic radiation at the output.6. An electron tunneling device comprising: a) first and secondnon-insulating layers spaced apart from one another such that a givenvoltage can be applied across the first and second non-insulatinglayers; and b) an arrangement disposed between the first and secondnon-insulating layers and configured to serve as a transport ofelectrons between and to said first and second non-insulating layers,said arrangement including i) a first insulating layer such that usingonly said first insulating layer would result in a given degree ofnonlinearity in said transport of electrons, with respect to said givenvoltage, ii) a different, second insulating layer disposed directlyadjacent to and configured to cooperate with said first insulating layersuch that the transport of electrons includes, at least in part,transport by means of tunneling, and such that said nonlinearity in thetransport of electrons, with respect to said given voltage, is increasedover and above said given degree of nonlinearity by the inclusion ofsaid second insulating layer without the necessity for any additionallayers, and iii) a third layer of material configured to furtherincrease said nonlinearity in the transport of electrons, with respectto said given voltage, over and above said given degree of nonlinearity.7. An electron tunneling device comprising: a) a first arrangementincluding first and second non-insulating layers spaced apart from oneanother such that a given voltage can be applied across the first andsecond non-insulating layers and configured to form an antenna; and b) asecond arrangement disposed between the first and second non-insulatinglayers and configured to serve as a transport of electrons between andto said first and second non-insulating layers, said arrangementincluding i) a first insulating layer such that using only said firstinsulating layer would result in a given degree of nonlinearity in saidtransport of electrons, with respect to said given voltage, and ii) adifferent, second insulating layer disposed directly adjacent to andconfigured to cooperate with said first insulating layer such that thetransport of electrons includes, at least in part, transport by means ofhot electron tunneling, and such that said nonlinearity in the transportof electrons, with respect to said given voltage, is increased over andabove said given degree of nonlinearity by the inclusion of said secondinsulating layer without the necessity for any additional layers.
 8. Amodulator for modulating an input electromagnetic radiation incidentthereon and providing a modulated electromagnetic radiation at anoutput, said modulator comprising: a voltage source for providing amodulation voltage, which modulation voltage is switchable between firstand second voltage values; a first arrangement including first andsecond non-insulating layers spaced apart from one another such that themodulation voltage can be applied across the first and secondnon-insulating layers; and a second arrangement disposed between thefirst and second non-insulating layers and configured to serve as atransport of electrons between and to said first and secondnon-insulating layers as a result of the modulation voltage, saidarrangement including at least a first insulating layer configured suchthat the transport of electrons includes, at least in part, transport bymeans of tunneling, with respect to the modulation voltage, wherein saidfirst arrangement further includes an antenna structure configured forabsorbing a given fraction of the input electromagnetic radiation with agiven value of absorptivity, while a remainder of the inputelectromagnetic radiation is reflected by the antenna structure, saidabsorptivity being defined as a ratio of an intensity of the givenfraction to a total intensity of the input electromagnetic radiation,and wherein said second arrangement is further configured to cooperatewith the first arrangement such that the antenna structure exhibits afirst value of absorptivity, when said first voltage value of modulationvoltage is applied across the first and second non-insulating layers,and exhibits a distinct, second value of absorptivity, when said secondvoltage value of modulation voltage is applied across the first andsecond non-insulating layers, thereby causing the antenna structure toreflect a different amount of the input electromagnetic radiation to theoutput as modulated electromagnetic radiation having a given value ofcontrast ratio, with respect to the modulation voltage, said contrastratio being defined as a ratio of said first value of absorptivity tosaid second value of absorptivity.
 9. The modulator of claim 8 whereinsaid antenna structure is formed from said first and secondnon-insulating layers.
 10. The modulator of claim 8 wherein said secondarrangement further includes a different, second layer disposed directlyadjacent to and configured to cooperate with the first insulating layersuch that said modulated electromagnetic radiation provided at theoutput has another value of contrast ratio, which is higher than saidgiven value of contrast ratio.
 11. A field effect transistor forreceiving an external signal, switching an input signal according to thereceived, external signal and providing an output signal, said externalsignal being switchable between a first value and a second value, saidfield effect transistor comprising: a diode structure including i) asource electrode for receiving said input signal, ii) a drain electrodespaced apart from said source electrode such that a given voltage can beapplied across the source and drain electrodes, and iii) an arrangementdisposed between the source and drain electrodes and configured to serveas a transport of electrons between and to said source and drainelectrodes, said arrangement including at least a first insulating layerconfigured such that the transport of electrons includes, at least inpart, transport by means of tunneling with a given value of a tunnelingprobability, a shielding layer at least partially surrounding said diodestructure; and a gate electrode disposed adjacent to said shieldinglayer, said gate electrode being configured to receive said externalsignal and to apply said external signal as said bias voltage acrosssaid source and drain electrodes such that, when said first value ofexternal signal is received at the gate electrode, a first signal valueis provided as the output signal at the drain electrode and, when saidsecond value of external signal is received at the gate electrode, asecond signal value is provided as the output signal at the drainelectrode and said output signal exhibits a given output ratio, whichoutput ratio is defined as the ratio of the first signal value to thesecond signal value.
 12. The field effect transistor of claim 11 whereinsaid arrangement is configured such that, using only said firstinsulating layer results in a first value of output ratio exhibited bythe output signal, and wherein said arrangement further includes adifferent, second layer disposed directly adjacent to and configured tocooperate with said first insulating layer such that the output signalexhibits a second value of output ratio, which second value of outputratio is higher than said first value of output ratio.